Many of our users have uploaded PDF files to SharePoint document libraries but it would always show up with a generic file icon and was difficult to distinguish what type of file it was as the document libraries store other files that have the generic file icon:
To get the PDF icon showing in SharePoint 2010 we had to do the following:
1. Download the small PDF logo from http://www.adobe.com/images/pdficon_small.gif
2. Save the file in the in C:/Program Files/Common Files/Microsoft Shared/Web Server Extensions/14/TEMPLATE/IMAGES/
3. Navigate to C:/Program Files/Common Files/Microsoft Shared/Web Server Extensions/14/TEMPLATE/XML and open DOCICON.xml in notepad that has been run as administrator, otherwise you may have problems saving back the file.
4. It is a good idea at this time to make a backup of the file by simply copying it to another location.
5. Add the line <Mapping Key=”pdf” Value=”pdficon_small.gif”> where the other mapping key entries are and save back the file.
6. Open a command prompt as administrator and type in IISRESET and press enter.
After the IISRESET has been performed you the PDF files should be showing the icon:
Please note that if you have more than one server in your SharePoint farm then you will need to repeat the steps above for each server.